For automobiles with power assisted door locks, the doors of the automobile are locked or unlocked by a locking mechanism operated by a motor provided in a door. Door locking or unlocking is accomplished by operating a switch inside the door when a driver is sitting in the driver's seat. To lock or unlock the door from outside the automobile, the driver places a key into a key hole provided in the door and turns the key.
Recently, systems have been used that lock or unlock the doors by remote operation from nearby the automobile using a remote control apparatus which comprises a transmitter and a receiver. The transmitter of the remote control apparatus may be provided in the grip of the ignition key or in the key holder. The receiver is provided inside the automobile.
FIG. 11 shows a block diagram of a transmitter T and a receiver R of a remote control apparatus. The transmitter T comprises an operation circuit 41, a decoder 42, a modulator 43, a carrier signal generator 44 and a light-emitting circuit 45. The receiver R comprises a light-receiving circuit 46, an amplifier 47, a demodulator 48, a decoder 49 and a code discriminating circuit 50. A door lock controller 51, connected to the code discriminating circuit 50, controls the locking or unlocking of the doors.
When a transmission switch 52, provided in the circuit 41 of the transmitter T is depressed, an identification code (hereinafter called "ID code") stored in the transmitter T is output to the modulator 43 from the decoder 42. The modulator 43 receives a carrier signal at a predetermined frequency (e.g., 38 kHz) from the carrier signal generator 44. Then, the modulator 43 modulates the frequency of the ID code with the carrier signal and outputs it as a modulation signal to the light-emitting circuit 45. The light-emitting circuit 45 produces an infrared signal from the modulation signal and transmits it to the receiver R.
The light-receiving circuit 46 in the receiver R provided inside the automobile, receives the modulated infrared-ray signal sent from the light-emitting circuit 45 of the transmitter T, and outputs this signal to the amplifier 47. The amplifier 47 amplifies the modulated signal to a predetermined level, and outputs it to the demodulator 48. The demodulator 48 extracts only the ID code from the signal and demodulates it to obtain a reception signal. This reception signal is output to the decoder 49. The decoder 49 decodes the reception signal to a reception code and outputs it to the code discriminating circuit 50.
The code discriminating circuit 50 compares the reception code with a discrimination code stored previously in the receiver R. When the reception code does not coincide with the discrimination code, the code discriminating circuit 50 erases the reception code and stands by until the next reception code is input. When the reception code coincides with the discrimination code, the code discriminating circuit 50 outputs a signal to the door lock controller 51 to unlock the doors when the doors are locked, or another signal to lock the doors when the doors are unlocked.
Recently, Audio-Visual machines and electric home appliances can be manipulated by a single "smart" remote controller. This "smart" or "learning" remote controller is designed to store an ID code (data) transmitted from a remote controller supplied with each machine. There are three ways that the learning remote controller stores the ID data of each machine. First, demodulation at a predetermined frequency is triggered by an operation signal from the transmitter of each machine, data compression is performed, and then the compressed data is stored in a memory area. Second, a modulation frequency is detected at the beginning of the operation signal, all signals are demodulated at that modulation frequency, data compression is performed, and the compressed data is stored in the memory area. Third, the frequency of the operation signal sent from the transmitter is determined. If this frequency is equal to or higher than a predetermined frequency, then a modulation system is assumed or considered as "learned". The modulation frequency and operation signal are demodulated and are stored in the memory area by the learning remote controller. When the frequency of data is below a specific frequency, it is assumed or "learned" that a baseband system exists. The ON/OFF periods of time for each data is measured and stored in the memory by the remote controller. With regard to the transmitter of a vehicle, the ID code may easily be stored or copied by the above methods. This unfortunately allows people other than the owner of the vehicle to unlock the doors.
Generally, the memory area of the learning remote controller has a relatively small capacity to store compressed data. If information is transmitted that causes the capacity of the memory area to overflow, the data cannot be stored. For the above type of learning remote controllers, if the signal at the beginning portion of the operation signal has a frequency different from the modulation frequency, any subsequent signal cannot be correctly read.
Accordingly, it is a primary objective of the present invention to provide a remote control apparatus which prevents an identification code from being stored in a learning remote controller.
It is another objective of this invention to provide a remote control apparatus which can more surely prevent an identification code from being stored in a learning remote controller.